Melting and sintering processes often produce a slag overlay. Slag removal can be challenging, especially when the metal or other material being formed must be successively layered to form a repair, cladding, or layered fabrication. Manually removing slag between each layer is slow and unproductive.
Submerged arc welding (SAW), electroslag welding (ESW), selective laser melting (SLM) and selective layer sintering (SLS) have been used to produce welds, cladding, and parts by additive manufacturing. In submerged arc welding a granulated flux buries an arc between an electrode wire or strip and a substrate to protect the molten material from reaction with the atmosphere. The process leaves slag on the surface of the metal deposit that must be removed before subsequent welding passes are made over or beside the existing deposit. The slag is manually removed, and unused granulated flux is vacuumed and combined with new flux for further processing. This process is also used for submerged arc cladding. Electroslag welding or cladding avoids an arc by providing molten flux at the point of processing as a current conductor. Other processing technologies include laser cladding and selective laser melting (SLM) or selective laser sintering (SLS) of feedstock powder.
Vacuuming can be employed in submerged arc welding to recover both slag and unused flux if the slag is readily dislodged from the deposit surface. However, when physical engagement is required to dislodge the slag, vacuuming is not enough. For powder bed processing (e.g. SLM, SLS), vacuuming tends to remove feedstock powder together with, or in preference to, slag because the powder is lighter and is not adhered to the substrate. Not only does this fail in slag removal, but it removes unused feedstock needed for additional melting/sintering passes on or beside the previous deposit.